With a known motor control device for controlling a motor such as a motor for an induction motor, a DC brush motor, and a brushless motor, an electric current command value is inputted from a superior controller every control cycle of a predetermined interval (e.g., 1 ms), an electric voltage command value is calculated based on the electric current command value, and a driving electric voltage according to the electric voltage command value is generated to be supplied to a coil of the motor. With the foregoing known motor control device, an actual electric current at the coil of the motor is detected by an electric current sensor, an electric current deviation between the actual electric current and the electric current command value is obtained, and a predetermined calculation transaction is applied to an integrated value of the electric current deviation (i.e., electric current deviation integrated value) to obtain the electric voltage command value. The electric voltage command value is sent to a PWM (Pulse Width Modulation) control portion. The PWM control portion generates a PWM pulse by switching a direct current voltage supplied from a direct current power source by a switching element of an inverter circuit to output the PWM pulse to the motor.
In order to simplify the control, generally, the electric current command applied with 3-to-2 phase conversion is inputted in the motor control device and the reverse conversion is applied (2-to-3 phase conversion) when determining the PWM pattern with a three-phase DC motor.
With the known motor control device, the electric current deviation between the actual electric current and the electric current command value is integrated every control cycle to obtain the electric voltage command value based on the integrated value (electric current deviation integrated value). Notwithstanding, the construction of the inverter circuit limits the electric voltage supplied to the motor in accordance with PWM pulse with the known motor control device.
In other words, the electric voltage supplied from the inverter circuit to the motor coil is either an electric voltage (i.e., ON) supplied from the direct current power source or 0V (i.e., OFF) momentarily. Accordingly, with the know motor control device, an objective output electric voltage is obtained as a whole by adjusting an ON time and an OFF time in one control cycle by switching the switching element. In case approximately sine wave formed electric current is supplied to the motor coil, the output electric voltage needs to be adjusted depending on the phase of the motor electric current.
On the other hand, the electric current deviation integrated value may increase irrelevant to the electric voltage (i.e., the average electric voltage of the PWM pulse) supplied to the motor depending on the operational conditions and the load at the motor. This raised a drawback at the control when the motor is suddenly stopped and the rotational direction of the motor rotating with high load is suddenly reversed. For example, in case the operation of the mechanical brake at an emergency stop and the sudden stop of the motor by the contact between the obstacle and a driven member of the motor, the back electromotive force generated by the motor rotation is suddenly vanished. Thus, the overvoltage may be applied by the excessive electric current deviation integrated value to generate the abnormal overcurrent. In case the rotational direction of the motor rotating with high load is suddenly reversed and the rotation of the motor is suddenly decreased, the control is likely to work to rotate the motor at the direction to reduce the electric current deviation integrated value (i.e., the same direction with the previous rotational direction) until the electric current deviation integrated value returns to the normal value, which may generate the delay of the response.
A need thus exists for a motor control device which has a less response delay without generating the abnormality at the sudden motor stop and at the reverse of the motor rotation.